The invention described herein relates to the field of seismic sources in marine geophysical operations. More particularly, the invention relates to a unique marine seismic source using a slotted cylinder piezoelectric transducer to generate low frequency seismic source energy.
Marine seismic vessels tow vibrators, air guns, explosives and other acoustic projector techniques to generate seismic source energy in marine geophysical operations. The seismic source energy is represented by a pressure pulse in the water. The pressure pulse generated travels downwardly through the water and underlying geologic structures and is reflected from interfaces between the geologic structures. The reflected signal impulses return to the water column and are detected with sensors towed behind the seismic vessel or positioned on the water bottom.
Source signals for marine geophysical operations are typically generated with acoustic sources such as compressed air guns. U.S. Pat. No. 4,180,139 to Walker (1979), U.S. Pat. No. 4,285,415 to Paitson (1981), and U.S. Pat. No. 5,228,010 to Harrison (1993) disclosed different mechanisms for discharging compressed air into water to generate acoustic source energy.
U.S. Pat. No. 3,896,889 to Bouyoucos (1975) disclosed a mass oscillation system for generating acoustic source energy in water. Other devices generate an acoustic signal by transmitting high velocity water jets in the underwater water environment. U.S. Pat. No. 4,131,178 to Buoyoucos (1978) and U.S. Pat. No. 4,153,135 to Bouyoucos (1975) disclosed a moveable piston for generating high velocity water jets.
Acoustic energy sources have been developed for sonar and other vessel detection systems. U.S. Pat. No. 4,651,044 to Kompanek (1987) disclosed a sonar transducer formed having a plurality of sectionalized piezoelectric elements attached to the interior wall of a slotted cylinder. Each element was constructed with a ceramic material having piezoelectric characteristics and was bonded with adhesive to the interior cylinder wall. An array of slotted cylinder segments in different rotational orientations were encapsulated in a boot and were filled with oil to prevent water intrusion. The orientation and placement of the piezoelectric elements on the interior cylinder walls controlled the orientation of the generated acoustic energy. In another embodiment, the piezoelectric elements were oriented linearly across the slotted cylinder internal diameter and were attached to the cylinder interior walls at opposite sides of the cylinder interior.
Other variations and improvements to acoustic energy sources have been developed. U.S. Pat. No.5,122,992 to Kompanek (1992) disclosed a transducer member having a closure member extending in a U-shaped configuration, and U.S. Pat. No. 5,267,223 to Flanagan et al. (1993) disclosed a compliant cover bonded to a transducer shell.
Conventional seismic sources require distribution of compressed air which adds weight and frictional drag to towed arrays. Existing slotted cylinder acoustic energy sources for underwater vessel detection operate at frequencies and power ranges unsuitable for geophysical operation. Accordingly, there is a need for an improved seismic source generator for use in marine seismic operations. The generator should be adaptable to different source energy requirements and should be easy to manufacture and deploy.